<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8">
    <title>Example</title>
</head>

<body>
    <script type="text/javascript">
    var myData = {
        name: "Adam",
    };

    document.writeln("Var: " + myData.weather);
    document.writeln("Prop: " + ("weather" in myData));

    myData.weather = "sunny";
    document.writeln("Var: " + myData.weather);
    document.writeln("Prop: " + ("weather" in myData));

    myData.weather = null;
    document.writeln("Var: " + myData.weather);
    document.writeln("Prop: " + ("weather" in myData));
    </script>
</body>

</html>
